Keep in mind that most likely the water will end up on the passenger side carpet near the door sill no matter where it is coming from. It could be the rear window, the seal around the door, the cab light, AC drain, windshield, heater core, etc. If the radiator water level goes down in time I might expect the heater core. I pulled the seats and all of the carpet. I then had a friend move a garden hose all over the cab while I watched from inside. I found the rear window was leaking, the seal around the passenger door was leaking, and the windshield was leaking due to a faulty install of a replacement about a year ago. The carpet has insulation attached to the underside of it. When I pulled the carpet I was surprised how much water it was holding in it. I bet it had a gallon absorbed in it. It took two days in the warm sun to finally dry.